1. Field of the Invention
The present invention is directed to a display tube and more specifically relates to a composition for a filming layer formed at the fluorescent surface of a display tube such as a cathode ray tube or a fluorescent display tube.
2. Description of the Prior Art
The fluorescent surface of a cathode ray tube generally comprises a layer coated with red, blue and green phosphor material deposited on a glass panel. Normally, a film layer is formed over the phosphor layer and then provided with a metal backing. However, the paste used in the phosphor layer through the normal printing process usually contains, as a binder, an acrylic or polyester resin which is soluble in an organic solvent and, accordingly, an aqueous emulsion lacquer or spray lacquer generally employed in cathode ray tubes or the like cannot be used for forming the material of the film over the phosphor layer since the phosphor layer repels water. In view of the foregoing, there has been proposed a method for forming a film layer in which the binder of the organic solvent type contained in the phosphor layer is removed by heat and thereafter, a thin aqueous layer is formed thereover. A solution of a resin dissolved in an organic solvent is spread as a thin film over the layer and then water is eliminated after hardening the film. However, this method has the disadvantage of increasing the number of steps and the cost of manufacture.